1. Field of the Invention
The present invention relates to an image recording apparatus, and more particularly it pertains to an image recording apparatus wherein an image is recorded on a recording medium supported on and transported by a transport member, by ejecting ink droplets from plural ink ejection ports provided in recording heads.
2. Description of the Related Art
In an image recording apparatus of the inkjet type in which an image is recorded on paper (recording medium) by ejecting ink droplets from recording heads, a printing system called a serial scan system is widely used primarily for personal use, wherein the paper is transported and printing is performed on a line-by-line basis by reciprocally moving recording heads in a direction perpendicular to the transporting direction of the paper. In recent years, a so-called full-line head type image recording apparatus adapted for office use as well has come to be manufactured wherein image recording is performed by continuously transporting paper and using a paper-width size, non-scan type recording head having a multiplicity of ink ejection ports (nozzles) arrayed along a direction (widthwise direction) perpendicular to the transporting direction of the paper, thereby achieving an increased printing speed.
Among the above image recording apparatuses is one in which either a transport belt for transporting paper attracted thereto or a roller about which the transport belt is entrained is provided with a rectilinear (one-dimensional) scale extending along the direction of rotational movement (paper transporting direction) of the transport belt or the direction or rotation of the roller, and a drive motor is controlled based on a measurement amount obtained by measuring the speed and movement amount of the scale by means of a sensor, thereby increasing transport and positioning accuracy (for example, refer to JP-A No. 8-152917). Further, among the above image recording apparatuses are ones in which a recording shift in the paper transporting direction due to a mounting position shift between plural line heads is corrected by adjusting the output timing of a recording signal on an each line head basis (for example, refer to JP-A No. 2002-248744), and one in which plural pixel blocks in image data are realigned according to the inclinations of line heads so that the inclinations of the line heads are corrected (influence of mounting error is reduced), thereby facilitating registration control when plural line heads are used (for example, refer to JP-A No. 2001-30478).
However, in the above image recording apparatuses, the position of the paper is shifted from an ideal position or a predicted position for the recording head due to a position shift (speed change) in the transporting direction of the transport belt for transporting the paper attracted and attached thereto or a position shift (skew/walk(meandering)) in a direction perpendicular to the transporting direction so that shading and/or distortion is caused to occur in the image, which leads to a decrease in image quality. Regarding such decrease in image quality due to speed change and/or skew/walk, techniques disclosed in the above Japanese patents prevent a decease in image quality due to speed change, but cannot prevent a decrease in image quality due to skew/walk.
Further, with a system in which paper is transported by being attracted and attached to a conventional transport belt, since the orientation of the paper attracted to the transport belt is not detected, it is very likely that recording is performed outside the paper, or on the transport belt when the paper is inappropriately attracted to the transport belt such as when the paper is obliquely attracted and attached to the transport belt, so that such problems arise as ink contamination inside the apparatus and useless ink consumption.